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This paper describes the recent imaging advances by Elphel, supplier of open source (hardware and software) cameras to customers that include Google (for select Street View and book scanning projects). It should interest imaging engineers, fans of open source, and those curious about open source hardware.

The paper was written by Dr. Andrey Filippov, the Russian physicist who founded Elphel in 2001. Filippov has contributed many papers to LinuxDevices through the years, as regular readers will be aware.

This paper begins with some background on Elphel, and Filippov's decision to build a company around open source. It then describes the evolving open source software stack used in Elphel's camera's, “from verilog to PHP.”

Along the way, Filippov painstakingly explains recent work done to improve the data pathway in the camera. As a result of the improvements, the newest Elphel cameras are less prone to dropping frames when image parameters are adjusted, he says. Though, very low-powered devices, the cameras are said to capture 5Mpix images (2592×1936) at 15fps, or 2MPix images (1920×1088) at 30fps.

It gets better after that, as Filippov includes a fairly mind-boggling description of the image compression algorithms used in Elphel cameras. He provides instructions for calculating the number of electrons each of your camera sensor's pixels can hold before welling over, and then provides a javascript calculator to use that “full well capacity” FWC figure, along with several other specifications, to determine the effective bit depth of your sensor. Based on the effective depth, an encoding strategy can be worked out.